Internal communication focuses on your own team, board and internal stakeholders. It's about alignment: what is the goal, who does what, when does what need to be ready. External communication focuses on attendees, partners or the press. It's about attraction: what can they expect and why is this not to be missed.
Internal communication starts earlier and needs a lot of repetition so everyone is on the same page. External communication varies per message and builds up to the event. Live Impact guides both.